Kim Hyun-Ki, Park Jeong Su, Sung Heungsup, Kim Mi-Na
Department of Laboratory Medicine, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Korea.
Ann Lab Med. 2015 May;35(3):298-305. doi: 10.3343/alm.2015.35.3.298. Epub 2015 Apr 1.
The modified Hodge test (MHT) was designed to detect carbapenemase-producing Enterobacteriaceae (CPE). This study evaluated variables to improve the performance of MHT.
Carbapenem-resistant Enterobacteriaceae isolated from November 2010 to March 2013 at the Asan Medical Center, were evaluated, including 33 metallo-β-lactamase (MBL) producers and 103 non-CPEs. MHT was performed by using two carbapenem disks (ertapenem and meropenem; Becton Dickinson, USA), three media (Mueller-Hinton agar (MHA), MacConkey agar (MAC), and zinc-enriched MHA), and two inoculums (0.5-McFarland [McF] suspension and a 10-fold dilution of it.) PCR was performed to detect β-lactamase genes of the MBL, AmpC, and CTX-M types.
The sensitivity of MHT for detecting New Delhi metallo-β-lactamase (NDM) producers was highest using ertapenem and 0.5-McF, 52.0% on MHA and 68.0% on MAC, respectively. NDM-producing Klebsiella pneumoniae (NDMKP) were detected with higher sensitivity on MAC (78.6%) vs. MHA (28.6%) (P=0.016), but VIM-producing Enterobacter, Citrobacter, and Serratia were detected with higher sensitivity on MHA (78.5%) vs. MAC (14.3%) (P=0.004). MBL producers were consistently identified with lower sensitivity using meropenem vs. ertapenem, 39.4% vs. 60.6% (P=0.0156), respectively. The effects of zinc and inoculum size were insignificant. Enterobacter aerogenes producing unspecified AmpC frequently demonstrated false positives, 66.7% with ertapenem and 22.2% with meropenem.
The MHT should be adjusted for the local distribution of species and the carbapenemase type of MBL producers. MAC and ertapenem are preferable for assessing NDMKP, but MHA is better for VIM. Laboratory physicians should be aware of the limited sensitivity of MHT and its relatively high false-positive rate.
改良 Hodge 试验（MHT）旨在检测产碳青霉烯酶肠杆菌科细菌（CPE）。本研究评估了可提高 MHT 性能的变量。
对 2010 年 11 月至 2013 年 3 月在峨山医学中心分离出的耐碳青霉烯肠杆菌科细菌进行评估，包括 33 株产金属β-内酰胺酶（MBL）菌株和 103 株非 CPE 菌株。使用两种碳青霉烯类药敏纸片（厄他培南和美罗培南；美国 Becton Dickinson 公司）、三种培养基（穆勒-欣顿琼脂（MHA）、麦康凯琼脂（MAC）和富锌 MHA）以及两种接种物（0.5 麦氏浊度[McF]悬液及其 10 倍稀释液）进行 MHT。进行 PCR 检测 MBL、AmpC 和 CTX-M 型β-内酰胺酶基因。
使用厄他培南和 0.5 McF 时，MHT 检测新德里金属β-内酰胺酶（NDM）产生菌的敏感性最高，在 MHA 上分别为 52.0%，在 MAC 上为 68.0%。产 NDM 的肺炎克雷伯菌（NDMKP）在 MAC 上的检测敏感性（78.6%）高于 MHA（28.6%）（P = 0.016），但产 VIM 的肠杆菌属、柠檬酸杆菌属和沙雷菌属在 MHA 上的检测敏感性（78.5%）高于 MAC（14.3%）（P = 0.004）。使用美罗培南与厄他培南相比，MBL 产生菌的鉴定敏感性始终较低，分别为 39.4%和 60.6%（P = 0.0156）。锌和接种量的影响不显著。产未明确类型 AmpC 的产气肠杆菌经常出现假阳性，使用厄他培南时为 66.7%，使用美罗培南时为 22.2%。
MHT 应根据当地菌种分布和 MBL 产生菌的碳青霉烯酶类型进行调整。MAC 和厄他培南更适合评估 NDMKP，但 MHA 对 VIM 更好。实验室医生应意识到 MHT 的敏感性有限及其相对较高的假阳性率。
